1. Field of the Invention
The present invention relates to a Liquid Crystal Display (hereinafter, referred to as LCD) and, more particularly, to an In Plane Fringe Field Switching Mode LCD wherein a counter electrode and a pixel electrode are formed on the same layer.
2. Description of the Prior Art
In TN (Twisted Nematic) mode LCD, liquid crystal molecules are twisted in 90° by the voltage applied to a counter electrode on an upper substrate and a pixel electrode on a lower substrate, thereby realizing display. The TN mode LCD has advantages that it is easy to drive and the fabrication process is simple. However, it also has disadvantages that viewing angle is narrow and response time is slow, thereby there are limitations in its application.
Therefore, In Plane Switching (hereinafter, referred to as IPS) mode LCD has been proposed to solve the problem of the TN mode. The IPS mode LCD has advantages of wide viewing angle and rapid response time, however, it has disadvantages of low aperture ratio and transmittance due to the fact that counter and pixel electrodes are made of opaque metals.
In order to overcome low aperture ratio and transmittance of the IPS mode LCD, a Fringe Field Switching (hereinafter, referred to as FFS) mode LCD has been proposed by the present applicant. In the FFS mode LCD, the counter electrode and the pixel electrode are made of transparent metals, for example, ITO and the distance between the counter electrode and the pixel electrode is narrower than a cell gap, thereby realizing high brightness and wide viewing angle.
And, the present applicant also has proposed an In Plane Fringe-Field Switching (hereinafter, referred to as IP-FFS) mode LCD realizing high screen quality by arranging the counter and pixel electrodes on the same layer.
FIG. 1 is a plan view showing the electrode structure of conventional IP-FFS mode LCD.
Referring to FIG. 1, a gate bus line 12 and a data bus line 16 are cross-arranged. A thin film transistor 17 is arranged at the intersection of the gate bus line 12 and the data bus line 16, as a switch. A common bus line 14 is arranged on the center of unit pixel defined by the gate bus line 12 and the data bus line 16, being parallel with the gate bus line 12.
A counter electrode 18 and a pixel electrode 19 are formed on the same layer by ITO patterning, respectively including bodies 18a, 19a and a plurality of branches 18b, 19b, 19c. The branches of counter electrode and pixel electrode 18b, 19b are alternately arranged, having a predetermined angle symmetric with respect to the common bus line 14. The counter electrode 18 is in contact with the common bus line 14. The pixel electrode 19 is in contact with the thin film transistor 17, further including a center branch 19c on the upper part of common bus line 14, being parallel with the common bus line. The center branch 19c is formed in order to form storage capacitance.
In the IP-FFS mode LCD, the counter electrode and the pixel electrode are arranged on the same layer by ITO patterning, thereby having advantages in afterimages and cost reduction, compared with FFS mode LCD wherein the counter electrode has a plate structure and the pixel electrode has a slit structure, arranged on the different layers. And, in the IP-FFS mode LCD, the counter electrode and the pixel electrode are arranged in the unit pixel to form two domains, thereby preventing color shift generation.
As a result, the IP-FFS mode LCD has advantages in afterimages and cost reduction, compared with the FFS mode LCD, thereby realizing high screen quality.
However, in the IP-FFS mode LCD, a short may be generated between the counter electrode and the pixel electrode since they are formed on the same layer. In order to prevent the short generation, branches of counter electrode and pixel electrode are arranged with a distance of over 3 μm. The body of counter electrode also maintains the same distance with the branch end of pixel electrode and the body of pixel electrode maintains the same distance, over 3 μm, with the branch end of counter electrode.
When the body of counter electrode and the branch end of pixel electrode, and the body of pixel electrode and the branch end of counter electrode are arranged with a good distance, electric fields are formed between each body and branch end. The direction of electric field corresponds to initial arrangement of rubbed liquid crystal molecules. Therefore, liquid crystal molecules are not twisted in the regions between the body of each electrode and the branch end thereof, thereby lowering transmittance of the IP-FFS mode LCD.